stamford as440

8/7/2019 STAMFORD AS440

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AS440 AUTOMATIC VOLTAGEREGULATOR (AVR)

SPECIFICATION INSTALLATION AND ADJUSTMENTSGeneral description Technical specification

AS440 is a half wave phase controlled thyristor type AVRand forms part of the excitation system for a brushlessgenerator. The design employs Surface Mount Technology(SMT) for high integration of features in a small footprintAVR.

Positive voltage build up from residual levels is ensured bythe use of efficient semiconductors in the power circuitry ofthe AVR. The power and voltage sensing circuits haveseparate terminals, allowing the excitation power to bederived directly from the stator winding for basicapplications or from an auxiliary winding if sustained short

circuit performance is required.

The AVR is linked with the main stator windings and theexciter field windings to provide closed loop control of theoutput voltage with load regulation of +/- 1.0%.

The AVR voltage sensing terminals continuously samplethe output windings for voltage control purposes. Inresponse to this sample voltage, the AVR controls thepower fed to the exciter field, and hence the main field, tomaintain the machine output voltage within the specifiedlimits, compensating for load, speed, temperature andpower factor, of the generator.

A frequency measuring circuit continually monitors thegenerator output and provides under-speed protection ofthe excitation system, by reducing the output voltageproportionally with speed below a pre-settable threshold. Amanual adjustment is provided for factory setting of theunder frequency roll off point, (UFRO). This can easily bechanged to 50 or 60 Hz in the field by push-on linkselection.

Over excitation conditions are limited to a safe period by aprotection circuit within the AVR.

Provision is made for the connection of a remote voltagetrimmer, allowing the user fine control of the generator's

output.

An analogue input is provided allowing connection to thePower Factor controller or other external devices withcompatible output.

The AVR has the facility for droop CT connection, to allowparallel running with other similarly equipped generators.

SENSING INPUTVoltage Jumper selectable

100-130 Vac 1 phase or190-264 Vac 1 phase

Frequency 50-60 Hz nominalPOWER INPUT

Voltage 100-264 V ac 1 phaseFrequency 50-60 Hz nominal

OUTPUTVoltage 82 V d.c. @ 200 V a.c.Current continuous 4A (see note 1).

transient 7.5A for 10 secs.Resistance 15 ohms min

(10 ohms min when inputvolts is less than 175 ac)REGULATION

+/- 1.0% (see note 2)THERMAL DRIFT

0.03% per deg. C change in AVR ambient (see note 3)TYPICAL SYSTEM RESPONSE

AVR response 20 msFiled current to 90% 80 msMachine Volts to 97% 300 ms

EXTERNAL VOLTAGE ADJUSTMENT+/-10% with 1 k ohm 1 watt trimmer (see note 4)Increasing resistance lowers voltage.

UNDER FREQUENCY PROTECTIONSet point 94 -98% Hz (see note 5)

UNIT POWER DISSIPATION

12 watts maximumBUILD UP VOLTAGE4 Volts @ AVR terminals

ANALOGUE INPUTMaximum input +/- 5 Vdc (see note 6)Sensitivity 1V for 5% Generator Volts (adjustable)Input resistance 1k ohm

QUADRATURE DROOP INPUT10 ohms burdenMax. sensitivity: 0.07 A for 5% droop 0PFMax. input: 0.33 A

OVER EXCITATION PROTECTIONSet point 65 V dcTime delay 10-15 seconds (fixed)

ENVIRONMENTALVibration 20-100 Hz 50mm/sec

100Hz 2kHz 3.3gOperating temperature -40 to +70C (note 7)Relative Humidity 0-70C 95% (note 8)Storage temperature -55 to +80C

NOTES1. De-rate by 12% if mounted in portrait orientation.2. With 4% engine governing.3. After 2 minutes.4. Generator de-rate may apply. Check with factory.5. Factory set, semi-sealed, jumper selectable.6. Any device connected to the analogue input must be fully

floating (galvanically isolated from ground), with aninsulation strength of 500V ac.

7. De-rate output current by 5% per degree C above 60C.8. Non condensing.


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DESIGN DETAIL

The main functions of the AVR are:

Potential Divider and Rectifier takes a proportion of thegenerator output voltage and attenuates it. The potentialdivider is adjustable by the AVR Volts potentiometer andexternal hand trimmer (when fitted). The output from thedroop CT is also added to this signal. A rectifier convertsthe a.c. input signal into d.c. for further processing.

The DC Mixer adds the Analogue input signal the Sensingsignal.

The Amplifier (Amp) compares the sensing voltage to theReference Voltage and amplifies the difference (error) toprovide a controlling signal for the power devices. TheRamp Generator and Level Detector and Driver infinitelycontrol the conduction period of the Power Control Devicesand hence provides the excitation system with the required

power to maintain the generator voltage within specifiedlimits.

The Stability Circuit provides adjustable negative acfeedback to ensure good steady state and transientperformance of the control system.

The Low Hz Detector measures the period of eachelectrical cycle and causes the reference voltage to bereduced approximately linearly with speed below apresettable threshold. A Light Emitting Diode givesindication of underspeed running.

The Synchronising circuit is used to keep the RampGenerator and Low Hz Detector locked to the generator

waveform period.

The Low Pass Filter prevents distorted waveformsaffecting the operation of the AVR control circuit.

The Short Circuit Detector senses the presence of ashort circuit on the generator output and forces thePower Control Devices into full conduction. This onlyoccurs when the AVR is powered from an auxiliarywinding.

Power Control Devices vary the amount of exciter fieldcurrent in response to the error signal produced by theAmplifier.

Suppression components are included to prevent subcycle voltage spikes damaging the AVR componentsand also to reduce the amount of conducted noise onthe generator terminals.

The Over Excitation Detector continuously monitors theexciter field voltage and provides signals, to collapsethe output voltage if an over excitation conditionpersists for the specified time period.

The Power Supply provides the required voltages forthe AVR circuitry.

Suppression

Low PassFilter

SynchronisingCircuit

Low HzDetection

PowerControlDevices

LevelDetector &

Driver

ReferenceVoltage

StabilityCircuit

PotentialDivider &Rectifier

Powersupply

RampGenerator

Generator

Amp

VoltageSensing

HandTrimmer

ExciterField

DCMixer

AnalogueInput

Droop

Short circuitDetector

Overexcitationdetector


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FITTING AND OPERATING

SUMMARY OF AVR CONTROLS

CONTROL FUNCTION DIRECTION

VOLTS TO ADJUST GENERATOR OUTPUT VOLTAGE CLOCKWISE INCREASES OUTPUT VOLTAGE

STABILITY TO PREVENT VOLTAGE HUNTING CLOCKWISE INCREASE THE DAMPING EFFECT

STAB SWITCH TO OPTIMISE TRANSIENT PERFORMANCE SEE TABLE ABOVE

UFRO TO SET THE UFRO KNEE POINT CLOCKWISE REDUCES THE KNEE POINT FREQUENCYDROOP TO SET THE GENERATOR DROOP TO 5% AT 0PF CLOCKWISE INCREASES THE DROOP

VTRIM TO OPTIMISE ANALOGUE INPUT SENSITIVITY CLOCKWISE INCREASES THE GAIN OR SENSITIVITY

EXC TRIP TO SET OVER EXCITATION TRIP CUT OFF LEVEL CLOCKWISE INCREASES THE CUT OFF LEVEL

ADJUSTMENT OF AVR CONTROLS

VOLTAGE ADJUSTMENT

The generator output voltage is set at the factory, butcan be altered by careful adjustment of the VOLTScontrol on the AVR board, or by the external handtrimmer if fitted. If major adjustment is necessary or

you lose stability, follow the VOLTAGE SETUPPROCEDURE.Terminals 1 and 2 on the AVR will be fitted with a shortinglink if no hand trimmer is required. Terminals La and Lb arelinked only for special low voltage applications.

WARNING! Do not increase the voltage above the ratedgenerator voltage. If in doubt, refer to the rating platemounted on the generator case.

WARNING! Do not ground any of the hand trimmerterminals as these could be above earth potential. Failureto observe this could cause equipment damage.

WARNING!If a replacement AVR has been fitted or re-setting of theVOLTS adjustment is required, turn the VOLTS controlfully anti-clockwise before running generator.

VOLTAGE SETUP PROCEDURE

For major adjustments and replacing the AVR.Read and understand this procedure beforeattempting to follow it.

1. Before running generator, turn the VOLTS controlfully anti-clockwise.2. Turn remote volts trimmer (if fitted) to midwayposition.3. Turn STABILITY control to midway position.4. Connect a suitable voltmeter (0-300V ac) acrossline to neutral of the generator.5. Start generator set, and run on no load at nominalfrequency e.g. 50-53Hz or 60-63Hz.6. If the red Light Emitting Diode (LED) is illuminated,refer to the Under Frequency Roll Off (UFRO)adjustment.7. Carefully turn VOLTS control clockwise until ratedvoltage is reached.8. If instability is present at rated voltage, refer tostability adjustment, then re-adjust voltage ifnecessary.9. Voltage adjustment is now completed.

REFER TO GENERATOR WIRING DIAGRAMFOR CONNECTION DETAILS

F2 F1 7 8 8 Z2

S1S2A1A2

AS440

Trim

Droop

Volts

StabilitySelection

UFRO

FrequencySelection

Indicator LEDStab

60Hz50Hz

123LbLa

ABCD

Stability Selection Table

No. Power range Response

B-D < 100kW SlowA-C < 100kW Fast

B-C 100-550kW FastA-B > 550kW Fast

Hand trimmer terminals. Remove

link before fitting hand trimmer.Link must be fitted when handtrimmer is not required.

ExcTrip

8 and Z2 linked fornormal operation


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FITTING AND OPERATING

STABILITY ADJUSTMENT

The AVR includes a stability or damping circuit to providegood steady state and transient performance of the

generator.

A switch is provided to change the response of thestability circuit to suit different frame size generators andapplications. The table shows the options available.The slow response settings may prove helpful inreducing lamp flicker.

The correct setting of the Stability adjustment can befound by running the generator at no load and slowlyturning the stability control anti-clockwise until thegenerator voltage starts to become unstable.

The optimum or critically damped position is slightly

clockwise from this point (i.e. where the machine voltsare stable but close to the unstable region).

UNDER FREQUENCY ROLL OFF (UFRO)ADJUSTMENT

The AVR incorporates an underspeed protection circuitwhich gives a volts/Hz characteristic when the generatorspeed falls below a presettable threshold known as the"knee" point.

The red Light Emitting Diode (LED) gives indication thatthe UFRO circuit is operating.

The UFRO adjustment is preset and sealed and onlyrequires the selection of 50/60Hz using the jumper link.

For optimum setting, the LED should illuminate as thefrequency falls just below nominal, i.e. 47Hz on a 50Hzsystem or 57Hz on a 60Hz system.

DROOP ADJUSTMENT

Generators intended for parallel operation are fitted witha quadrature droop C.T. which provides a power factordependent signal for the AVR. The C.T. is connected toS1, S2 on the AVR.

The DROOP adjustment is normally preset in the worksto give 5% voltage droop at full load zero power factor.

Clockwise increases the amount of C.T. signal injectedinto the AVR and increases the droop with lagging powerfactor (cos ). With the control fully anti-clockwise thereis no droop.

TRIM ADJUSTMENT

An analogue input (A1 A2) is provided to connect to aPower Factor Controller or other devices. It is designed to

accept dc signals up to +/- 5 volts.

WARNING!Any devices connected to this input mustbe fully floating and galvanically isolated from ground,with an insulation capability of 500 Vac. Failure toobserve this could result in equipment damage.

The dc signal applied to this input adds to the AVR sensingcircuit. A1 is connected to the AVR 0 volts. Positive on A2increases excitation. Negative on A2 decreases excitation.

The TRIM control allows the user to adjust the sensitivity ofthe input. With TRIM fully anti-clockwise the externallyapplied signal has no effect. Clockwise it has maximum

effect.

Normal setting is fully clockwise when used with a PowerFactor Controller.

OVER EXCITATION (EXC TRIP) ADJUSTMENT

The adjustment is set and sealed in the works and shouldnot be altered.An over excitation condition is indicated on the commonLED which also indicates under speed running.The generator must be stopped to reset an over excitationcondition.

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